The central pool of IPv4 addresses officially ran dry on Tuesday after the Internet Assigned Numbers Authority (IANA) allocated the last remaining blocks of address space.

APNIC, which provides internet addressing services to the Asia Pacific region, received two /8s (33 million addresses) on Tuesday in a move that triggered the immediate distribution of the last five /8s to Regional Internet Registries. ISPs and businesses are rapidly burning through any IPv4 addresses APNIC makes available, so organisations in the region are expected to be among the first to feel the effects of IPv4 exhaustion.

The organisation tracking the allocation of IPv4 declared 1 February X-Day (exhaustion day), conjuring images of Mad Max-style battles over the last remaining supplies of gasoline IPv4 addresses.

In reality, the exhaustion of IPv4 has long been predicted but has remained a distant prospect until recently thanks to the use of Network Address Translation (NAT) technology, which meant banks of corporate PCs all sat behind small ranges of IP addresses. Many units of internet real estate are still sparsely used, with only around 14 per cent actually been utilised, according to a study by the University of Southern California, published on Tuesday.

John Heidemann, leader of a team at the USC Viterbi School of Engineering Information Sciences Institute that carried out the study, commented: "As full allocation happens, there will be pressure to improve utilization and eventually trade underutilized areas."

Unwrapping the hairball that is IP address allocation on the net in order to make use of this untapped resource will be far from easy. In the short term many businesses and ISPs will be able to get by by layering NAT devices, but the long term solution is to move to IPv6, the next generation Internet Protocol.

Better utilization, trading, and other strategies can recover "twice or four times current utilisation" of IPv4, according to Heidemann, who admits that trading our way out of trouble is only a short-term solution. "Requests for address double every year, so trading will only help for two years," he said.

IPv6 offers a vastly expanded address space but even though it's been around for a decade it remains unsupported on many networks. That needs to change or else the interweb will become fragmented in the 21st century equivalent of a canals and railways transport system. ®